The present invention relates to location of a xe2x80x9chot spotxe2x80x9d in a patient""s body tissue, particularly a vein.
The need for accurate location of a patient""s vein for the purpose of medical procedures is well known. The task can be relatively simple when a needle must be inserted into a superficial vein but the procedure can be hit and miss in those cases wherein it is necessary to locate veins which are several millimeters beneath the skin surface. Known techniques usually rely on effecting a local increase in blood pressure by application of a tourniquet so as to cause protuberance of the veins but this is not always effective and, in any case, is apt to be unsuitable other than for superficial veins.
U.S. Pat. No. 4,817,622 (Pennypacker et al.) discloses an infrared imager for viewing subcutaneous location of vascular structures based upon the infrared radiation of a patient""s limb. A video camera which is sensitive to infrared radiation produces a video image highlighting contrasting portions of the flesh which are infrared absorbing or infrared scattering. This permits location of those veins which would otherwise be hard to find.
U.S. Pat. No. 5,608,210 (Esparza et al.) describes a device for aiding a technician to locate a vein for inserting a hypodermic needle therein, again based on the infrared radiation of an appropriate area of the flesh so as to highlight the location of a subcutaneous vein. The resulting heat contour, which allows the vein to be highlighted, is imaged using an infrared-sensitive video camera and the image is displayed so as to allow the ready location of the vein.
Likewise, U.S. Pat. No. 5,519,208 (also to Esparza et al.) discloses a method and apparatus for gaining intravenous access wherein, again, a source of radiation is required for irradiating an area of the patient. The wavelength of the radiation is such that the radiation is absorbed in areas containing veins and reflected in all other areas whereby an image of the irradiated area permits the irradiated vein to be readily contrasted from the surrounding area.
All of the above-referenced patents have in common the provision of an external source of infrared radiation and the subsequent display of the resulting heat contour, which permits the vein to be highlighted. Such an approach requires not only an external source of infrared radiation but, moreover, expensive infrared imaging and display apparatus.
U.S. Pat. No. 5,678,555 (O""Connell) discloses a non-invasive method for locating blood vessels in a live human body using infrared scanning and imaging techniques to distinguish relative temperature differences between blood carrying vessels and surrounding human tissue. An infrared imaging camera is used to detect the emissions of an object to differentiate the specific elevated surface temperature associated with blood vessels in a human body and surrounding tissue. The veins can then be marked. O""Connell thus obviates the need for an external source of infrared radiation but his temperature profile is displayed qualitatively in the form of an infrared thermal image allowing a hotspot to be seen visually by an operator of the infrared imaging camera.
DE 30 20 359 (Hermann) discloses a procedure for the capture and display of thermographs of biological or technical structures, whereby in addition to the display of the local temperature distribution, the temperatures at each pixel of a thermograph are digitally captured and displayed on a TV monitor. Although digital imaging is employed, no digital processing is suggested and hot spots are displayed qualitatively using color variations to distinguish between different temperatures of the scanned tissue.
It thus emerges that whilst both U.S. Pat. No. 5,678,555 and DE 30 20 359 disclose passive thermal imaging techniques, they both display the resulting temperature profile qualitatively in a visual manner, thus allowing a hot spot to be identified from the thermal image. In practice, a hot spot may relate to a single vein or to multiple veins in close proximity and neither of these references is capable of distinguishing whether the hot spot is indicative of a single vein or of multiple veins. Still less can these references actually distinguish between the veins themselves in the event that a hot spot relates to multiple veins in close mutual proximity and having variable depth distribution. Therefore, whilst they will correctly mark a lone vein, they are liable to miss the most suitable vein when it is one of multiple veins in close mutual proximity. This is a significant drawback particularly bearing in mind that a priori there is no way to distinguish from the thermal image whether a hot spot relates to a single vein or to multiple veins in close mutual proximity.
It is therefore an object of the present invention to provide an instrument, which locates and marks a vein for the purpose of allowing accurate alignment of a needle therewith or any other medical procedure.
According to a broad aspect of the invention there is provided a portable passive instrument for locating and marking at least one area of a person""s body tissue having a local variation in temperature compared with surrounding body tissue, said instrument comprising:
temperature scanning means for scanning along the person""s skin within a region of said body tissue so as to obtain signals representative of a temperature profile along an unstimulated portion of the skin,
processing means coupled to said temperature scanning means for analyzing said signals so as to derive the temperature profile in order to determine said at least one area having local temperature variation, and
marking means for marking said at least one area;
characterized in that:
the temperature scanning means is adapted for scanning along at least a line of skin within the region of said body tissue so as to obtain discrete signals representative of respective temperatures of discrete points along an unstimulated portion of the at least a line of skin,
the processing means is further adapted to process the temperature profile by determining first and second derivatives of the temperature profile in order to compensate for a possible influence of multiple veins in close mutual proximity so as to determine a location of each vein within the scanned region of body tissue, and
the marking means is adapted to mark at least one vein within the scanned region of body tissue.
The marking means may be a point of light, which is directed on to the skin so as to allow automatic alignment of an injection needle therewith. Alternatively, it can mark the location of the vein with a small spot of ink so as to allow subsequent manual injection.
Preferably the temperature scanning means includes an infrared detector for detecting infrared radiation having a wavelength of between 3-20 xcexcm and includes suitable folding optics for allowing the skin to be scanned.